A crack resistant layer with good binder fracture energy properties and method of selecting same

ABSTRACT

A method of selecting a crack resistant layer to be applied to an existing surface, the method comprising the steps of: selecting at least one bituminous binder to examine, where the bituminous binder comprises bitumen and one or more polymers, where the one or more polymers include a sufficient amount of conjugated diene such that at least 2.5% of the bituminous binder&#39;s weight comprises conjugated diene, preferably at least 3.0%. more preferably at least 3.5%, and most preferably 4.0%; forming at least one bituminous mixture comprising the bituminous binder and an aggregate; testing each bituminous binder for binder fracture energy properties; and selecting a bituminous binder for use in the crack resistant layer. The method may further comprise the steps of testing the bituminous mixture for fatigue properties and selecting the bituminous binder for use in the crack resistant layer based on fatigue properties and binder fracture energy properties, and/or testing the bituminous mixture for fracture energy and selecting the bituminous binder for use in the crack resistant layer based on mixture fracture energy properties and bituminous binder fracture energy properties.

FIELD OF THE INVENTION

The present invention relates to a crack resistant layer with goodbinder fracture energy properties and a method of selecting same. Moreparticularly, the present invention relates to a bituminous binder witha critical amount of conjugated diene, which allows for enhanced binderfracture energy properties in a crack resistant layer.

DESCRIPTION OF THE RELATED ART

When pavements deteriorate, they may be overlaid with hot mix asphalt(HMA) to repair them. When designing an overlay, the rate of crackpropagation through the overlay, the rate of deterioration of thereflective crack, and the amount of water that can infiltrate throughthe cracks must be considered. One disadvantage with such HMA overlaysis that cracks in the old pavement reflect through the new overlay. Torelieve this reflective cracking, thicker overlays may be placed.Another disadvantage with these overlays is that they typically have alow strain tolerance and a low resistance to reflective cracking.

To improve traditional HMA overlays, asphalt binders that display theability to undergo creep or stress relaxation at low temperatures may beused. Such bituminous binders minimize the potential for thermal andreflective cracking. However, the disadvantage with such bituminousbinders is that they are highly ductile and have a low shear modulus athigh temperatures, and thus roads created with them tend to rut.Asphalts with high shear modulus that resist rutting at hightemperatures may also be used. However, such binders tend to be brittleat low temperatures, and thus roads created with them tend to crack.Typical asphalt bituminous binders formulated for pavement applicationsusually display either high shear modulus at high temperatures or highductilities at low temperatures but not both.

A typical highway HMA surface mixture has about 3% to 5% air voids and afatigue life of only about 500 cycles when tested at 15° C. with astrain amplitude of 2,000 microstrains and frequency of 10 Hz using a4-point bending beam apparatus. The best surface mixture with about 3%to 5% air voids has a fatigue life of only about 2,000 to 5,000 cycleswhen tested at 15° C. with a strain amplitude of 2,000 microstrains andfrequency of 10 Hz using a 4-point bending beam apparatus. Othermixtures with air voids greater than 5% to 7% may have a fatigue life ofonly about 500 to 1,500 cycles when tested at 15° C. with a strainamplitude of 2,000 microstrains and frequency of 10 Hz using a 4-pointbending beam apparatus.

Blankenship et al., U.S. Pat. No. 6,830,408, which is incorporatedherein by reference, attempts to solve the foregoing problems throughthe use of an interlayer that is placed on the cracked road underneaththe overlay. The interlayer includes a mixture of aggregate andbituminous binder, preferably polymer modified asphalt, and is used todelay or stop the occurrence of cracking, control crack severity, reduceoverlay thickness, and enhance waterproofing capabilities. Theinterlayer is highly strain tolerant and substantially impermeable.

The bituminous binder used in the interlayer of the '408 patent includesbitumen, one or more polymers, and, optionally, a cross-linking agent toeffect vulcanization of the polymer in the bitumen. Limitations on thecharacteristics of the bituminous binder and interlayer are set forth inthe '408 patent. In particular, the '408 patent specifies that thepercentage of air voids in the interlayer must be between 2.0% and 4.0%.This produces a flexural beam fatigue performance of at least 100,000cycles to failure.

The problem with such interlayers is that, in order to get such afatigue life and retard the progression of reflective cracks in thepavement, these interlayers sacrifice a degree of their load bearingcapacity, as measured in the Hveem stabilometer, and typically haveHveem stabilities of about 18-21. In order to compensate for their lowstability, these interlayers are placed below the top layers of apavement structure so that they are not exposed to direct traffic loads.Thicker top layers help to improve the total structural stability butare costly. Still further, the top layers of the pavement structurecannot completely compensate for the low load bearing capacity of theinterlayer.

Blankenship et al., U.S. application Ser. No. 10/631,149, which isincorporated herein by reference, attempts to solve this problem throughthe use of a highly strain tolerant, substantially moisture impermeable,hot mix reflective crack relief interlayer. The interlayer includes apolymer modified bituminous binder mixed with a dense fine aggregatemixture that is made primarily from manufactured sand. This results inincreased stability and improved load bearing capacity. Limitations onthe characteristics of the bituminous binder and interlayer are setforth in the '149 application. In particular, the '149 applicationspecifies that the percentage of air voids in the interlayer must bebetween 1.0% and 5.0%, preferably 2.0% to 4.0%, and most preferablyabout 3.0%. This produces a flexural beam fatigue performance of atleast 50,000 cycles to failure, preferably 80,000 and most preferably100,000.

The problem with this interlayer is that it is impermeable. When such aninterlayer is placed on Portland Cement Concrete (PCC) or another pavedsurface, the interlayer has the potential to trap vapor underneath it.As changes occur in climatic and environmental conditions, this causesthe PCC to release moisture or vent. The interlayer then rises, creatinga blister. This causes overlays on top of this interlayer also to riseand blister.

Blankenship et al., U.S. Pat. No.7,479,185, which is incorporated hereinby reference, attempts to solve this problem through the use of a layerthat remains substantially moisture impervious and retains its abilityto retard the formation of reflective cracks while having increasedvapor permeability. This layer may be an interlayer, but also may be abase layer or an overlay.

Limitations on the characteristics of the bituminous binder and layerare set forth in the '185 Patent. In particular, the '185 Patentspecifies that the percentage of air voids in the layer must be at least3.0%, preferably at least 4.0%, more preferably at least 4.5%, even morepreferably at least 5.0%, and most preferably at least 7.0%. Thisproduces a flexural beam fatigue performance of at least 5,000 cycles tofailure, preferably at least 35,000 cycles to failures and mostpreferably at least 100,000 cycles to failure. The '185 Patent notesthat there is typically an inverse relationship between the air voids ina bituminous mixture and fatigue resistance of that mixture. However,the bituminous mixture of the '185 Patent may be made by creating a verylarge amount of air voids in an aggregate structure and then filling alarge portion of those voids with bitumen. The total amount of air voidsis critical. Too many air voids will limit fatigue resistance and toofew air voids will compromise permeability.

The problem with the '185 layer is the narrow operating window. Theperfect aggregate structure is required to produce the skeletalstructure that meets the requirements of fatigue resistance, strength,and permeability. Local aggregates may not be suitable requiring morecostly aggregate sources to be used. Tight tolerances at the hot mixplants creates off-specification product that impacts costs.Additionally, a very high asphalt content is required, which increasescosts dramatically.

The current art uses mixture volumetric properties and film thickness toachieve acceptable beam fatigue properties. The '408 patent toBlankenship requires air voids in a tight and low range, extremely highbinder film thicknesses, and extremely low DP's (dust to effectivebinder ratio). The '149 application greatly limits aggregate propertiesto effect acceptable beam fatigue properties. The '185 Patent allows forhigher air void content but also requires a higher binder filmthickness. Hence, the current art is void of any binder property thataffects beam fatigue properties.

In each of the foregoing, polymer is used in the bituminous binder.Methods of preparing polymer modified bitumen is described in Maldonadoet al., U.S. Pat. No. 4,242,246, and Maldonado et al., U.S. Pat. No.4,330,449, both of which are incorporated herein by reference.

Notwithstanding the foregoing, there remains a need for a crackresistant layer with low air voids and good binder fracture energyproperties that does not suffer from the drawbacks of the layers of theBlankenship patents and application. Accordingly, it would be desirableto provide a bituminous binder for a crack resistant layer with greaterthan 1% air voids and binder fracture energy greater than 40 J/m², thatis stable, that does not require special aggregate structure orexcessive asphalt content, and that may be used as a base layer,interlayer or overlay.

SUMMARY OF THE INVENTION

In general, in a first aspect, the present invention relates to a methodof selecting a crack resistant layer to be applied to an existingsurface, the method comprising the steps of: selecting at least onebituminous binder to examine, where the bituminous binder comprisesbitumen and one or more polymers, where the one or more polymers includea sufficient amount of conjugated diene such that at least 2.5% of thebituminous binder's weight comprises conjugated diene, preferably atleast 3.0%, more preferably at least 3.5%, and most preferably 4.0%;forming at least one bituminous mixture comprising the bituminous binderand an aggregate; testing each bituminous binder for binder fractureenergy properties; and selecting a bituminous binder for use in thecrack resistant layer. The testing of the bituminous mixture for binderenergy may comprise testing a single edge notch beam tested at 0.1mm/sec at −30° C., calculated by ASTM D 5045-99 where the dimensions ofthe single edge notched beam are B=6.0 mm, W=9.5 mm, A=4.9 mm, andL=44.0 mm (all dimensions + or −1%), where the bituminous binder wasRTFO aged per AASHTO T-240, and the samples were conditioned at testtemperature for 18 to 20 hours before testing which may result in abituminous binder fracture energy of greater than 40 J/m², preferablygreater than 50 J/m², and most preferably greater than 60 J/m².

The method may further comprise the steps of testing the bituminousmixture for fatigue properties and selecting the bituminous binder foruse in the crack resistant layer based on fatigue properties and binderfracture energy properties. The testing of each bituminous mixture forfatigue properties may comprise subjecting each bituminous mixture to aflexural beam fatigue test performed at 2,000 microstrains, 10 Hz, and15° C. per ASTM D 7460-08. Such a flexural beam fatigue test may resultin at least 5,000 cycles to failure, preferably at least 10,000 cyclesto failure, and most preferably at least 15,000 cycles to failure.

The method may further comprise the steps of testing the bituminousmixture for fracture energy and selecting the bituminous binder for usein the crack resistant layer based on mixture fracture energy propertiesand bituminous binder fracture energy properties. Testing of thebituminous mixture for fracture energy may comprise subjecting thebituminous mixture to a Semi-Circular Bend Test or a Disc CompactTension Test. The fracture energy test may be the Disc Compact TensionTest performed at a temperature of −10° C. and a rate of loading of 1.0mm/min, in accordance with ASTM D 7313-07, and may result in a mixturefracture energy of greater than 600 J/m², preferably greater than 700J/m², and most preferably greater than 800 J/m². The preferred testingdevice is an RSA III Dynamic Mechanical Analyzer from TA Instruments,Inc of New Castle, Del.

The method may further comprise the steps of testing the bituminousmixture for permeability and selecting the bituminous binder for use inthe crack resistant layer based on binder fracture energy properties andpermeability. The bituminous mixture may be tested for permeability inaccordance with ASTM D 3637, which may result in permeability greaterthan 8 cm².

The bituminous mixture may have a Hveem stability of greater than 21 perASTM D 1560 and may have greater than 1% air voids. The bituminousbinder may further comprise additives, such as cross-linking agents,accelerators, extenders, fluxing agents, or combinations thereof. Theaggregate may comprise a hard and inflexible mineral aggregate, a hardand inflexible man-made aggregate, or a combination thereof. Thebituminous mixture may further comprise recycled materials, such asreclaimed asphalt pavement, glass, ground rubber tires, ceramics,metals, or mixtures thereof.

In a second aspect, the invention relates to a crack resistant layerhaving the properties set forth above.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a bituminous binder for use in a crackresistant layer. The layer may be used to resurface a distressedpavement surface, and may be used as a base layer, an interlayer, or anoverlay. Use of such a layer is described in the Description of RelatedArt section above and in the Blankenship patent and applications. Thebituminous binder is such that the crack resistant layer has good binderfracture energy properties. A method of selecting such a bituminousbinder is also provided herein.

The layer is formed from a bituminous mixture, which comprises thebituminous binder and an aggregate. The bituminous binder includesbitumen, one or more polymers, and, optionally, other additives,including but not limited to cross-linking, accelerators, extenders,fluxing agents, and/or other similarly appropriate additives suitablefor use in bituminous binders.

The polymer used in the bituminous binder may be any elastomer orplastomer suitable for use in bitumen, including but not limited tothose described in the Maldonado and Blankenship patents andapplication, and containing at least a critical amount of conjugateddiene. The critical amount of conjugated diene is at least 2.5%,preferably at least 3.0%, more preferably at least 3.5%, and mostpreferably 4.0%. Such high amounts of conjugated diene have notpreviously been used in similar layers because of the high cost of sucha relatively large polymer content and the difficulty to process.Surprisingly, it has been found that increasing the amount of conjugateddiene above the critical amount produces a layer with improved fatigueresistance of any asphalt-aggregate mixture. Thus, the life of the layeris increased, making the layer cost effective despite the large polymercontent.

The viscosity of the bituminous binder, one or more polymers, and,optionally, other additives should be less than about 5,000 cP at 135°C., preferably less than about 3,500 cP, and most preferably less thanabout 2,500 cP. High bituminous binder viscosity requires excessive mixtemperatures at the hot mix plant and lay down on the road.Additionally, excessive bituminous binder viscosity may requireextraordinary compactive effort on the road and could cause aggregatedegradation or excessive air voids in the resulting bituminous mixture.

The aggregate may be hard and inflexible mineral aggregates, such assand, stone, lime, Portland cement, kiln dust, or mixtures thereof; manmade hard and inflexible aggregates, such as wet bottom boiler slag,blast furnace slag, or mixtures thereof; or any other appropriateaggregate. The structure of the aggregate may be any of those describedin the Blankenship patent and applications, or may be any otherappropriate structure. The aggregate need not include manufactured sand,as required by the '149 Blankenship application.

Recycled materials, such as reclaimed asphalt pavement, glass, groundrubber tires, ceramics, metals, or mixtures thereof, or any otherappropriate recycled material may be incorporated into the mixture. Anyconjugated diene from a recycled vulcanizate is not considered as partof the bituminous binder and is not included in the critical amount ofconjugated diene as part of this invention.

The bituminous mixture formed from the appropriate amount of conjugateddiene bituminous binder and the aggregate may meet any local standardsfor traditional bituminous mixture properties such as VMA, VFA, density,dust to binder ratio, and the like. However, the Hveem stability perASTM D 1560 should be greater than 21 and the bituminous mixture shouldhave greater than 1% air voids. The bituminous mixture with suitablecrack resistance will have a bituminous binder fracture energy ofgreater than 40 J/m², more preferably greater than about 50 J/m², andmost preferably greater than about 60 J/m², a beam fatigue of greaterthan 5,000 cycles to failure, more preferably at least 10,000 cycles tofailure, and most preferably at least 15,000 cycles to failure; and amixture fracture energy of greater than 600 J/m², more preferablygreater than about 700 J/m², and most preferably greater than about 800J/m².

Generally, the method of selecting the bituminous binder for use in thecrack resistant layer involves mixing a bituminous binder and anaggregate to form a bituminous mixture, forming a specimen layer fromthe bituminous mixture, and testing the bituminous binder to determinebinder fracture energy. If the binder fracture energy is sufficient, thebituminous binder is appropriate for use in the crack resistant layer.If not, another bituminous binder must be used with higher conjugateddiene content, and the process must begin again. Additionally oralternately, the specimen layer may be tested for beam fatigue.Additionally or alternately, the bituminous mixture may be tested formixture fracture energy. In both instances, if the additional propertytested, namely beam fatigue or mixture fracture energy respectively, issufficient, the bituminous binder is appropriate for use in the crackresistant layer. If not, another bituminous binder must be used and theprocess must begin again. The bituminous mixture may also additionallyor alternately be tested for permeability, where the bituminous binderis appropriate only if the permeability is sufficient, and if not,another must be selected.

The bituminous binder and aggregate should meet the criteria set forthabove, and should be mixed in sufficient quantities that the bituminousmixture meets the criteria set forth above. In particular, thebituminous binder should include a polymer comprising at least 2.5%,preferably at least 3.0%, more preferably at least 3.5%. and mostpreferably at least 4.0% conjugated diene based on the weight of thepolymer modified bitumen. Furthermore, the bituminous binder should beformed in such a way that the viscosity is no more than about 5,000 cPat 135° C., preferably less than about 3,500 cP, and most preferablyabout 2,500 cP, and the bituminous mixture should be formed in such away that the specimen layer formed therefrom has at least 1% air voidsand a Hveem stability of at least 21.

The bituminous binder may be tested for fracture energy using anyappropriate test and any appropriate parameters. For example, whentesting a single edge notch beam at 0.1 mm/sec at −30° C. calculated byASTM D 5045-99 where the preferred dimensions of the single edge notchedbeam are B=6.0 mm, W=9.5 mm, A=4.9 mm, and L=44.0 mm, where thebituminous binder was RTFO aged per AASHTO T-240, and the samples wereconditioned at test temperature for 18 to 20 hours before testing, anappropriate bituminous binder should result in a bituminous binderfracture energy of greater than about 40 J/m², more preferably greaterthan about 50 J/m², and most preferably greater than about 60 J/m².

The specimen layer may be tested for fatigue, preferably using a beamfatigue test, most preferably using a flexural beam fatigue test. Aflexural beam fatigue test determines the number of times a specimen maybe flexed before it cracks. The test may be performed using anyappropriate parameters. For example, the test may be performed at 2,000microstrains, 10 Hz, and 15° C. per ASTM D7460-08. An appropriatebituminous binder should result in a layer having at least 5,000 cyclesto failure, preferably at least 10,000 cycles to failure, and mostpreferably at least 15,000 cycles to failure when tested at 2,000microstrains, 10 Hz, and 15° C. per ASTM D 7460-08.

The bituminous mixture may be tested for mixture fracture energy usingany appropriate test, such as a Semi-Circular Bend Test or a DiscCompact Tension Test, and also using any appropriate parameters. Forexample, when tested using a Disc Compact Tension Test performed at atemperature of −10° C., a rate of loading of 1.0 mm/min, and inaccordance with ASTM D 7313-07, an appropriate bituminous binder shouldresult in a bituminous mixture with a mixture fracture energy of greaterthan about 600 J/m², more preferably greater than about 700 J/m², andmost preferably greater than about 800 J/m².

The bituminous mixture may be tested for permeability in accordance withASTM D 3637, in which case, an appropriate bituminous binder shouldresult in a permeability of greater than about 8 cm².

Mixture volumetric properties and/or binder film thicknesses do not needto be strictly controlled to achieve desired properties. The system canbe optimized by choosing the lowest conjugated diene content thatachieved the desired mixture and/or binder properties. The type ofmixture, either coarse or fine, large aggregate of small, high or lowair voids content, can be brought into acceptable levels of a crackresistant layer by selecting a binder with the appropriate conjugateddiene content.

EXAMPLE 1

Eight polymer modified bituminous binders were created, four by heatinga Suncor PG64-22 bituminous binder, adding polymers, mixing sufficientlyto disperse the polymers within the bituminous binder, and adding asufficient amount of sulfur to cross-link. The other four were createdby the same process but with Suncor PG58-28 bituminous binder instead ofPG64-22 bituminous binder. The polymers used were Solprene 1205 withabout 75% conjugated diene, and Solprene 1110L with about 80% conjugateddiene available from Dynasol. Binders 1 through 8 are described inTables 1 and 2.

TABLE 1 Suncor PG 58-28 Solprene Solprene Conjugated Binder 1205 1110LDiene 1 0.00% 0.00% 0.00% 2 1.00% 1.00% 1.55% 3 2.00% 2.00% 3.10% 43.00% 3.00% 4.65%

TABLE 2 Suncor PG 64-22 Solprene Solprene Conjugated Binder 1205 1110LDiene 5 0.00% 0.00% 0.00% 6 1.00% 1.00% 1.55% 7 2.00% 2.00% 3.10% 83.00% 3.00% 4.65%

The eight bituminous binders were used to form eight bituminous mixtureswhich in turn were used to form eight specimen layers. Mixture gradationand general volumetric properties are set forth in Table 3.

TABLE 3 9.5 mm Mixture Gradation Sieve (mm) % Passing Mixture PropertiesAir Voids 4.0% 12.5 100 Pb 5.9% 9.5 100 VMA 15.0% 4.75 79.1 VFA 72.0%2.36 46.6 DP 1.2 1.18 30.4 0.6 19.7 0.3 12.5 0.15 7.5 0.075 5.7

The layers were tested at 2,000 microstrains, 1 0 Hz, and 15° C. perASTM D 7460-08 for beam fatigue. The results are set forth in Table 4:

TABLE 4 Beam Conjugated Fatigue Diene Binder (Cycles) Content Suncor PG58-28 1 815 0.00% 2 2,165 1.55% 3 4,419 3.10% 4 26,247 4.65% SuncorPG-64-22 5 91 0.00% 6 592 1.55% 7 523 3.10% 8 1,994 4.65%

As can be seen from Table 4, a higher percentage of conjugated dieneresulted in a higher number of cycles to failure. A logarithmiccorrelation coefficient (r²) between Beam Fatigue and conjugated dienecontent was 0.961 and 0.862 for the PG58-28 and PG64-22 bindersrespectively. The correlation surprisingly demonstrates the positiveeffect of conjugated diene on beam fatigue properties. If acceptablebeam fatigue properties are not achieved, another binder must be chosenwith higher conjugated diene content.

Each bituminous layer was tested for mixture fracture energy and wastested at a temperature of −10° C., a rate of loading of 1.0 mm/min, andin accordance with ASTM D 7313-07. The results are set forth in Table 5:

TABLE 5 Fracture Conjugated Energy Diene Binder (J/m²) Content Suncor PG58-28 1 699 0.00% 2 817 1.55% 3 1,150 3.10% 4 1,338 4.65% SuncorPG-64-22 5 434 0.00% 6 540 1.55% 7 671 3.10% 8 1,084 4.65%

A logarithmic correlation coefficient (r²) between Mixture FractureEnergy and conjugated diene content was 0.973 and 0.955 for the PG58-28and PG64-22 binders respectively. Similarly, the correlationsurprisingly demonstrates the positive effect of conjugated diene onmixture fracture energy properties. If acceptable mixture fractureenergy properties are not achieved, another binder must be chosen withhigher conjugated diene content.

Each Binder was evaluated for Bituminous Binder Fracture Energy andtested 0.1 mm/sec at −30° C. per ASTM D 5045-99 where the bituminousbinder was RTFO aged per AASHTO T-240, and the samples were conditionedat test temperature for 18 to 20 hours before testing. The results areset forth in Table 6:

TABLE 6 Binder Fracture Conjugated Energy Diene Binder (J/m²) ContentSuncor PG 58-28 1 9.31 0.00% 2 33.47 1.55% 3 46.45 3.10% 4 75.94 4.65%Suncor PG-64-22 5 10.70 0.00% 6 31.69 1.55% 7 46.15 3.10% 8 69.28 4.65%

As can be seen from Table 6, a higher percentage of conjugated dieneresulted in a higher binder fracture energy. A linear correlationcoefficient (r²) between conjugated diene content and Binder FractureEnergy was 0.980 and 0.993 for the PG58-28 and PG64-22 bindersrespectively. The correlation surprisingly demonstrates the positiveeffect of conjugated diene on binder fracture energy properties. Ifacceptable mixture binder fracture energy properties are not achieved,another binder must be chosen with higher conjugated diene content.

EXAMPLE 2

Four polymer modified bituminous binders were created, each by heating aPG64-22 bituminous binder, adding polymers, mixing sufficiently todisperse the polymers within the bituminous binder, and adding asufficient amount of sulfur to cross-link. The polymers used wereSolprene 1205 with about 75% conjugated diene available from Dynasol andSolprene 411 with about 70% conjugated diene available from Dynasol. Thefirst bituminous binder was a control and contained no conjugated diene.The second bituminous binder contained 1.7% Solprene 1205 and 0.3%Solprene 411, resulting in 1.49% total conjugated diene based on theweight of the polymer modified bituminous binder. The third bituminousbinder contained 3.4% Solprene 1205 and 0.6% Solprene 411, resulting in2.97% total conjugated diene based on the weight of the polvmer modifiedbituminous binder. Finally, the fourth bituminous binder contained 5.1%Solprene 1205 and 0.9% Solprene 411, resulting in 4.46% total conjugateddiene based on the weight of the polymer modified bituminous binder.Binders 9 through 12 of are described in Tables 7.

TABLE 7 PG 64-22 Bitumen Solprene Solprene Conjugated Binder 1205 411Diene Content 9 0.00% 0.00% 0.00% 10 1.70% 0.30% 1.49% 11 3.40% 0.60%2.97% 12 5.10% 0.90% 4.46%

The four bituminous binders were used to form bituminous mixtures, whichin turn were used to form eight specimen layers. Mixture gradation andgeneral volumetric properties are set forth in Table 8 and 9.

TABLE 8 9.5 mm Mixture Gradation Sieve (mm) % Passing Mixture PropertiesAir Voids 4.0% 12.5 100 Pb 7.0% 9.5 99.6 VMA 15.9% 4.75 88.7 VFA 75.4%2.36 62.5 DP 1.1 1.18 40.4 0.6 23.4 0.3 13.3 0.15 7.9 0.075 6.0

TABLE 9 4.75 mm Mixture Gradation Sieve (mm) % Passing MixtureProperties Air Voids 4.0% 12.5 100 Pb 6.9% 9.5 100 VMA 15.8% 4.75 97.8VFA 75.0% 2.36 77.4 DP 1.9 1.18 56.9 0.6 38.5 0.3 21.5 0.15 11.9 0.0759.9

Each bituminous layer was tested for mixture fracture energy and wastested at a temperature of −10° C., a rate of loading of 1.0 mm/min, andin accordance with ASTM D 7313-07. The results are set forth in Table10:

TABLE 10 Mixture Fracture Energy (J/m²) Conjugated Diene Content 0.00%1.49% 2.97% 4.46% 4.75 mm Mixture 345 438 615 1,371 9.5 mm Mixture 463508 1,559 2,190

A logarithmic correlation coefficient (r²) between Mixture FractureEnergy and conjugated diene content was 0.903 and 0.922 for the 9.5 mmand 4.75 mm mixtures respectively. The correlation not only demonstratesthe positive effect of conjugated diene on mixture fracture energyproperties, it also demonstrates the ability of the binder alone tocontrol mixture fracture energy by increasing the conjugated dienecontent until acceptable properties are achieved.

Each Binder was evaluated for Bituminous Binder Fracture Energy andtested 0.1 mm/sec at −30° C. per ASTM D 5045-99 where the bituminousbinder was RTFO aged per AASHTO T-240, and the samples were conditionedat test temperature for 18 to 20 hours before testing. The results areset forth in Table 11:

TABLE 11 Binder Conjugated Fracture Diene Energy Content (J/m²) 0.00%23.7 1.49% 34.8 2.97% 41.8 4.46% 48.2

As can be seen from Table 11, a higher percentage of conjugated dieneresulted in a higher binder fracture energy. A linear correlationcoefficient (r²) between conjugated diene content and Binder FractureEnergy was 0.981. The correlation demonstrates the positive effect ofconjugated diene on binder fracture energy properties.

Alternative Mixtures:

A variety of alternate mixtures may be used to form the crack resistantlayer described herein, so long as the amount of conjugated diene andthe fatigue properties meet the requirements set forth above, as well asthe fracture energy properties if such properties are considered. Forexample, every state and the Federal Highway Administration have targetlevels for various types of mixes. These target levels may be used, andthe crack resistant properties of the mixture may be optimized byvarying the level of conjugated diene content using the method set forthabove. The charts below set forth three alternate mixtures, as requiredby the Texas Department of Transportation (Alternate Mixture #1), theOklahoma Department of Transportation (Alternate Mixture #2), and theNew Jersey Department of Transportation (Alternate Mixture #3).

Alternate Mixture #1 TxDOT Special Specification 3111 Crack AttenuatingMixture Sieve Size % Passing 2″ — Target Laboratory-  98* MoldedDensity, % 1½″ — Binder Content 6.5% minimum 1″ — Design VMA, % Minimum  16.0 ¾″ — Design VFA, % 73-76 ½″ — Dust/Binder Ratio 0.6-1.6 ⅜″ 98.0-100.0 Number of Gyrations 50 #4 70.0-90.0 #8 40.0-65.0 #1620.0-45.0 #30 10.0-30.0 #50 10.0-20.0 #200  2.0-10.0 *% Air Voids = (100− 98) = 2.0%

Alternate Mixture #2 Oklahoma DOT Special Provision for Ultra ThinBonded Wearing Course Sieve Size Type A Type B Type C ¾″ 100 ½″ 100 75-100 ⅜″ 100  75-100 50-80 #4 40-55 25-38 25-38 #8 22-32 19-27 19-27#16  15-25 15-23 15-23 #30  10-18 10-18 10-18 #0  8-13  8-13  8-13 #100  6-10  6-10  6-10 #200  4-6 4-6 4-6 Asphalt Content 5.0-6.2 4.8-6.24.6-6.2 Typical Design Air Voids   9-14%   9-14%   9-14%

Alternate Mixture #3 NJ DOT 902.03 Open-Graded Friction Course (OGFC)and Modified Open-Graded Friction Course Mixture Designations (%Passing) OGFC - MOGFC - MOGFC - Sieve Sizes 9.5 mm 12.5 mm 9.5 mm ¾″ 100½″ 100  85-100 100 ⅜″  80-100 35-60  85-100 No. 4 30-50 10-25 20-40 No.8  5-15 10-15 10-15 No. 200 2.0-5.0 2.0-5.0 2.0-4.0 Minimum 5.5 5.7 6asphalt binder, %¹ Minimum % 15% 20% 18% Air Voids, design Minimum lift¾″ 1¼″ ¾″ thickness, design Fiber 0.4 0.4 0.4 Stabilizer, % Ndesign 5050 50http://www.state.nj.us/transportation/eng/specs/2007/spec900.shtm#t90202031

From the above description, it is clear that the present invention iswell adapted to carry out the objects and to attain the advantagesmentioned herein as well as those inherent in the invention. Whilepresently preferred embodiments of the invention have been described forpurposes of this disclosure, it will be understood that numerous changesmay be made which will readily suggest themselves to those skilled inthe art and which are accomplished within the spirit of the inventiondisclosed and claimed.

1. A method of selecting a crack resistant layer to be applied to anexisting surface, the method comprising the steps of: selecting at leastone bituminous binder to examine, where the bituminous binder comprisesbitumen and one or more polymers, where the one or more polymers includea sufficient amount of conjugated diene such that at least 2.5% of thebituminous binder's weight comprises conjugated diene; forming at leastone bituminous mixture comprising the bituminous binder and anaggregate; testing each bituminous binder for binder fracture energyproperties; and selecting a bituminous binder for use in the crackresistant layer.
 2. The method of claim 1 where at least 3.0% of theweight of the bituminous binder comprises conjugated diene.
 3. Themethod of claim 1 where at least 3.5% of the weight of the bituminousbinder comprises conjugated diene.
 4. The method of claim 1 where atleast 4.0% of the weight of the bituminous binder comprises conjugateddiene.
 5. The method of claim 1 where the testing of the bituminousbinder for fracture energy comprises testing a single edge notch beamtested at 0.1 mm/sec at −30° C., calculated by ASTM D 5045-99 where thedimensions of the single edge notched beam are B=6.0 mm, W=9.5 mm, A=4.9mm, and L=44.0 mm where the bituminous binder was RTFO aged per AASHTOT-240, and the samples were conditioned at test temperature for 18 to 20hours before testing.
 6. The method of claim 5 where the fracture energytest results in a bituminous binder fracture energy of greater than 40J/m²
 7. The method of claim 5 where the fracture energy test results ina bituminous binder fracture energy of greater than 50 J/m².
 8. Themethod of claim 5 where the fracture energy test results in a bituminousbinder fracture energy of greater than 60 J/m².
 9. The method of claim 1further comprising the steps of testing the bituminous mixture forfatigue properties and selecting the bituminous binder for use in thecrack resistant layer based on fatigue properties and fracture energyproperties.
 10. The method of claim 9 where the testing of thebituminous mixture for fatigue properties comprises subjecting eachbituminous mixture to a flexural beam fatigue test performed at 2,000microstrains, 10 Hz, and 15° C. per ASTM D 7460-08.
 11. The method ofclaim 10 where the flexural beam fatigue test results in at least 5,000cycles to failure.
 12. The method of claim 10 where the flexural beamfatigue test results in at least 10,000 cycles to failure.
 13. Themethod of claim 10 where the flexural beam fatigue test results in atleast 15,000 cycles to failure.
 14. The method of claim 1 furthercomprising the steps of testing the bituminous mixture for fractureenergy and selecting the bituminous binder for use in the crackresistant layer based on mixture fracture energy properties andbituminous binder fracture energy properties.
 15. The method of claim 14where the testing of each bituminous mixture for fracture energycomprises subjecting the bituminous mixture to a Semi-Circular Bend Testor a Disc Compact Tension Test.
 16. The method of claim 15 where thefracture energy test is the Disc Compact Tension Test and is performedat a temperature of −10° C. and a rate of loading of 1.0 mm/min, inaccordance with ASTM D 7313-07.
 17. The method of claim 16 where thefracture energy test results in a mixture fracture energy of greaterthan 600 J/m².
 18. The method of claim 16 where the fracture energy testresults in a mixture fracture energy of greater than 700 J/m².
 19. Themethod of claim 16 where the fracture energy test results in a mixturefracture energy of greater than 800 J/m².
 20. The method of claim 1further comprising the steps of testing the bituminous mixture forpermeability and selecting the bituminous binder for use in the crackresistant layer based on binder fracture energy properties andpermeability.
 21. The method of claim 20 where the bituminous mixture istested for permeability in accordance with ASTM D
 3637. 22. The methodof claim 21 where the permeability is greater than 8 cm².
 23. The methodof claim 1 where the bituminous mixture has a Hveem stability of greaterthan 21 per ASTM D
 1560. 24. The method of claim 1 where the bituminousmixture has greater than 1% air voids.
 25. The method of claim 1 wherethe bituminous binder further comprises additives.
 26. The method ofclaim 25 where the additives comprise cross-linking agents,accelerators, extenders, fluxing agents, or combinations thereof. 27.The method of claim 1 where the aggregate comprises a hard andinflexible mineral aggregate, a hard and inflexible man-made aggregate,or a combination thereof.
 28. The method of claim 1 where the bituminousmixture further comprises recycled materials.
 29. The method of claim 31where the recycled materials are reclaimed asphalt pavement, glass,ground rubber tires, ceramics, metals, or mixtures thereof.
 30. A crackresistant layer to be applied to an existing surface, where the layercomprises: an aggregate; and a bituminous binder, wherein the bituminousbinder is comprised of bitumen and one or more polymers, where the oneor more polymers include a sufficient amount of conjugated diene suchthat at least 2.5% of the bituminous binder's weight comprisesconjugated diene; where the bituminous binder and the aggregate aremixed and form a bituminous mixture; and wherein the binder exhibitsdesirable fracture energy properties when subjected to testing for suchfracture energy properties.
 31. The crack resistant layer of claim 30where at least 3.0% of the weight of the bituminous binder comprisesconjugated diene.
 32. The crack resistant layer of claim 30 where atleast 3.5% of the weight of the bituminous binder comprises conjugateddiene.
 33. The crack resistant layer of claim 30 where at least 4.0% ofthe weight of the bituminous binder comprises conjugated diene.
 34. Thecrack resistant layer of claim 30 where the bituminous binder hasdesirable fracture energy properties if a single edge notch beam istested at 0.1 mm/sec. at −30° C., calculated by ASTM D 5045-99 where thedimensions of the single edge notched beam are B=6.0 mm, W=9.5 mm, A=4.9mm, and L=44.0 mm, where the bituminous binder was RTFO aged per AASHTOT-240, and the samples were conditioned at test temperature for 18 to 20hours before testing and results in a fracture energy of greater than 40J/m².
 35. The crack resistant layer of claim 30 where the bituminousbinder has desirable fracture energy properties if a single edge notchbeam is tested at 0.1 mm/sec. at −30° C., calculated by ASTM D 5045-99where the dimensions of the single edge notched beam are B=6.0 mm, W=9.5mm, A=4.9 mm, and L=44.0 mm, where the bituminous binder was RTFO agedper AASHTO T-240, and the samples were conditioned at test temperaturefor 18 to 20 hours before testing and results in a fracture energy ofgreater than 50 J/m².
 36. The crack resistant layer of claim 30 wherethe bituminous binder has desirable fracture energy properties if asingle edge notch beam is tested at 0.1 mm/sec. at −30° C., calculatedby ASTM D 5045-99 where the dimensions of the single edge notched beamare B=6.0 mm, W=9.5 mm, A=4.9 mm, and L=44.0 mm, where the bituminousbinder was RTFO aged per AASHTO T-240, and the samples were conditionedat test temperature for 18 to 20 hours before testing and results in afracture energy of greater than 60 J/m².
 37. The crack resistant layerof claim 30 where the layer exhibits beam fatigue properties of at least5,000 cycles to failure when subjected to a flexural beam fatigue testat 2000 microstrains at 10 Hz when tested 15° C. per ASTM D 7460-08. 38.The crack resistant layer of claim 30 where the layer exhibits beamfatigue properties of at least 10,000 cycles to failure when subjectedto a flexural beam fatigue test at 2000 microstrain at 10 Hz when tested15° C. per ASTM D 7460-08.
 39. The crack resistant layer of claim 30where the layer exhibits beam fatigue properties of at least 15,000cycles to failure when subjected to a flexural beam fatigue test at 2000microstrains at 10 Hz when tested 15° C. per ASTM D 7460-08.
 40. Thecrack resistant layer of claim 30 where the bituminous mixture is testedfor fracture energy properties with a Semi-Circular Bend Test or a DiscCompact Tension Test.
 41. The crack resistant layer of claim 40 wherethe fracture energy test is performed at a temperature of −10° C. and arate of loading of 1.0 mm/min., in accordance with ASTM D 7313-07. 42.The crack resistant layer of claim 41 where the fracture energy testresults in a mixture fracture energy of greater than 600 J/m².
 43. Thecrack resistant layer of claim 41 where the fracture energy test resultsin a mixture fracture energy of greater than 700 J/m².
 44. The crackresistant layer of claim 41 where the fracture energy test results in amixture fracture energy of greater than 800 J/m².
 45. The crackresistant layer of claim 30 where the bituminous mixture's permeabilityis greater than 8 cm² when tested in accordance with ASTM D
 3637. 46.The crack resistant layer of claim 30 where the bituminous mixture has aHveen stability of greater than 21 per ASTM D
 1560. 47. The crackresistant layer of claim 30 where the bituminous mixture has greaterthan 1% air voids.
 48. The crack resistant layer of claim 30 furthercomprising additives.
 49. The crack resistant layer of claim 48 wherethe additives comprise cross-linking agents, accelerators, extenders,fluxing agents, or combinations thereof.
 50. The crack resistant layerof claim 30 where the aggregate comprises a hard and inflexible mineralaggregate, a hard and inflexible man-made aggregate, or a combinationthereof.
 51. The crack resistant layer of claim 30 where the mixturefurther comprises recycled materials.
 52. The crack resistant layer ofclaim 51 where the recycled materials are reclaimed asphalt pavement,glass, ground rubber tires, ceramics, metals, or mixtures thereof.